I have used Prvi-Partizan/PPU Boxer Primed, Brass cased ammo for .223 and 7.62x54R. The brass is good, and it shoots well for me (although my rifles are accurate enough that even TulAmmo shoots well).
If you have thousands of rounds set away, what you actually have is a lot of moderately OK quality reloading components.
Buy yourself a collet puller die, a .30 caliber collet, a two-die set of .308 Full Length reloading dies, and a Dillon Square Deal reloading press. Pull the ammo down to components, they are certainly good enough to use as beginner's handloading/load development components. Essentially you will be doing load development with good (not premium, but actually quite good) primed brass, a consistent (but probably not replaceable with any commercially available) propellant, and military grade ball projectiles. There better ways to start reloading, but it's not an especially terrible approach with the proper in-person guidance.
Buy a current Sierra reloading manual that covers rifle calibers and start reading the entire book from cover to cover, repeating as needed. The real value if this manual is how well it covers all the aspects surrounding the actual load recipes. While loads may not be employed as printed, they can still give a basic sort of understanding about generic, ballpark load information.
The powder that's in the cartridges will likely be custom produced for PPU, but basic, conservative load development technique, combined with the mentoring of an experienced load developer (this part is essential), can set you on a productive path. As you pull the powder down, keep a keen eye on the granule size, color, and shape; it is not uncommon that cartridge manufacturers will change propellants between production runs. Try not to combine different types; keep and load develop them separately, also working out an average charge weight per cartridge using each type of powder. These averages will be the loads for your first batches of training/learning handloads. The odds are great that you can recombine those components into cartridges of significantly better accuracy in your own particular rifle than they started out originally.
This all may sound complicated and confusing, but with a good mentor, it can even turn into very valuable learning experiences. Normally, doing load development with Unknown, but compatible components is an advanced technique. In some ways, the only difference from conventional load development is that the lot of powder you'll be using is new to the reloader, but in those same ways, it really not all that different from working with known powder brands with published charge weights. If this falls outside your confidence range, keep the pulldown powder aside for later experimentation, after getting some experience under your belt. Keeping it in a dark, dry, uncontaminated state, under conditions that you yourself are comfortable with, will let you feel confident that the stored powder will be ready for you when you're ready for it. It is essential that you mark the powder containers with origin, application, and average charge weights for future reference, or you might otherwise be better off simply spreading it in a flower bed as a nitrate fertilizer. The primed cases and bullets can just as well be used with purchased compatible powders for learning the handloading techniques you will rely on afterward.
Greg
